Signal modulators are utilized in a number of applications, for instance as part of the conversion from analogue signals to digital signals or vice versa. For example sigma-delta (ΣΔ) modulators (SDM's) are a type of signal modulator that may be used to convert an input analogue signal into a pulse-density-modulated (PDM) signal comprising a series of digital ones and zeros at a fixed sample rate and the relative density of ones and zeros corresponds to the analogue signal's amplitude. However the fixed frequency inevitably introduces quantisation noise into the signal, and SDMs usually comprise also at least one functional operational amplifier.
Time-encoding modulators (TEMs) are modulators that encode input signals into a time-encoded data stream. One particular form of time-encoding is pulse-width modulation (PWM). In a PWM signal, an input value is encoded by the duration of a given output signal level, e.g. the duration or width of pulse of a first signal level, compared to the duration of any period(s) of any other signal level(s) in a cycle period. For a conventional two-level PWM signal, the input signal value may be encoded by the duty cycle of a pulse of a first signal level within the cycle period, i.e. the proportion of the cycle period spent at the first output signal level. Time-encoding modulators may encode an input signal into a PWM signal by comparing the input signal with a periodic reference signal, such as a triangular waveform to encode the input signal by the duration of pulses in the output signal. However this requires circuitry to generate an appropriately accurate periodic reference signal and/or operational amplifier circuitry.
In general there is a desire for smaller and/or lower power modulators that can be used, for example, as part of a signal converter such as an ADC or DAC.